During development, mammalian dermal fibroblasts are derived from distinct spatial locations, where the developing craniofacial dermis originates from ectoderm-derived cranial neural crest and paraxial mesoderm. Several syndromes with craniofacial defects possess mesodermal and ectodermal dysplasias, including under- and maldevelopment of the dermis, yet despite the critical role of the dermis in development and disease, there is little information about the mechanisms that govern the spatiotemporal control of gene expression to specify and maintain dermal cell fate on different sites of the body. Recently, microRNAs (miRNAs) have emerged as important post-transcriptional regulators of mammalian gene expression in several tissues with roles in cell fate specification, proliferation, differentiation, and communication. However, despite the advances in this emerging field, it is still not clear which specific miRNAs are required to regulate dermal development and physiology. The goal of our research is to elucidate the role of novel, key miRNAs as spatiotemporal regulators of mammalian craniofacial dermis development. In our preliminary studies, we have identified a small number of miRNAs that possess intriguing, restricted expression patterns in the developing craniofacial dermis during specific developmental time points, suggesting they may function to regulate some of the important transcription factors and other signaling molecules required for the specification and differentiation of the developing dermis. Importantly, two of these miRNAs are expressed from the same transcript derived from a long, non-coding RNA, that when mutated in mice, causes severe craniofacial and skeletal defects, including dermal hypoplasia. Our goal is to elucidate the function of these miRNAs in the early stages of dermal morphogenesis and define their requirement for craniofacial dermal cell fate specification and/or maintenance. I aim to define identify novel, physiological target genes of these candidate miRNAs, characterize their expression patterns throughout craniofacial development, and determine the contribution of these miRNAs to dermal fate specification and/or maintenance using genetic approaches. The findings from the proposed work will provide novel insight into the role of specific miRNAs during craniofacial development and reveal the molecular mechanisms that underlie patterning of the orofacial dermis, which when abrogated, result in craniofacial defects.